POTENTIALS AT PHASE BOUNDARIES 211 



in colloidal chemistr\'', were shown also to exercise their influence 

 upon the electric properties of membranes. Hober's studies fur- 

 nish valuable experimental data, and the important question at 

 present is whether these phenomena can be best explained in terms 

 of Hober's theory of perm.eability or by the theory of forces at the 

 phase boundary. Cremer^^ correlated the variable permeabihty 

 to ions in Ostwald's sense with the ionic mobilities, and regarded 

 these potentials as being analogous to diffusion potentials. He 

 identified the more diffusible ion as that ion which has a great mobility 

 in the medium into which it penetrates. It was also Cremer who 

 first succeeded in arranging experimentally a two-phase chain 

 without the use of metals, such as: 



Aqueous 

 solution 



Nitrobenzene 



Nitrobenzene 

 + picric acid 



Aqueous 

 solution 



In order to explain the observed potential differences in terms of 

 Cremer 's theory it. would be necessary to assume incredibly great 

 differences in the mobilities of the several ions involved. 



The phase boundary theories discussed in the preceding sections 

 represent a development the way to which had been paved by 

 Nernst's^^ electromotive theoiy of metal electrodes. The experi- 

 mental and theoretical investigations along this path were carried 

 out in a most thorough manner by Haber,"^" as well as previously 

 by Cremer, although with not quite the same interpretation. These 

 investigations were followed by those of Beutner referred to above 

 and which represent a distinct step in advance, inasnmch as they 

 can be dnectly apphed to the interpretation of bioelectric phenom- 

 ena. The place of origin of the electromotive forces is, accord- 

 ing to the latter author's conclusions, at the boundary surface lying 

 between aqueous phases and the lipoidal membranes of living cells 

 and tissues. And, indeed, all such electric phenomena become 

 easily exphcable by merely assuming that such membranes repre- 



'»M. Cremer, Zeitschr. f. Biol. 47, 1 (1906); Nagels Handb. d. Physiol. 

 4, 868 (1909). 



»9 W. Nernst, Zeitschr. f. physikal. Chem. 9, 140 (1S92); Nernst and Riesen- 

 feld, Ann. d. Physik. 8, 600 (1902). 



-°F. Haber, Ann. d. Physik. 25, 917 (1908); Haber and Klemensiewicz, 

 Zeitschr. f. physik. Chem. 67, 385 (1909). 



